112 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 



of the ship. Therefore, in order to get a good result, it was necessary 

 for the compass to have a very great gyrostatic resistance, so termed, 

 opposing energetically any force tending to change the direction of its 

 axis of rotation, and that the friction of its bearings should be made 

 as small as possible. A consequence of the latter condition, however, 

 would be that the gyrostat would come to its normal position only 

 after a relatively long time, oscillating to and fro about that normal 

 position. Meanwhile it would be subject to new perturbations. 



Accordingly one great desideratum was to provide some device for 

 lessening these oscillations; at first, Anschiitz tried for this purpose 

 a second gyrostat; later he developed a much more simple and effi- 

 cient method. His gyrostatic compass was tried on the steamer 

 Deutschland in 1908 and has since been used in the German Navy. 

 It has just been adopted by the English Navy, and other navies are 

 also trying it. 



Let us consider its principles: We know that a gyroscope once 

 started tends to maintain its axis in an invariable direction, and 

 that if any force is applied tending to change this direction, preces- 

 sional movement takes place, which displaces the axis perpendicular 

 to the direction of the disturbing force. Such being the case, let us 

 imagine a gyroscope, inclosed in an appropriate box, suspended from 

 a float which rests in a liquid bath in such a manner that the gyro- 

 scope is perfectly free to swing in any direction like a pendulum 

 which is at rest; the center of gravity of the system is below the 

 metacenter; the gyroscope is mounted at the lowest point possible. 

 Because of its weight the axis of the gyroscope tends to maintain 

 itself, as well as the whole attached mechanism, in a horizontal 

 position. 



Let us set the gyroscope disk rotating. In the past such rotation 

 could be effected only by rough and very unsatisfactory means; now 

 we have a much more advantageous method at our disposal. We 

 may, for instance, drive it by a little three-phase motor fed by means of 

 fine conducting wires so that the rotation may be kept up indefinitely. 



As soon as the gyroscope disk is in rapid rotation with its axis hori- 

 zontal, then if this axis is not in the plane of the terrestrial meridian, 

 the rotation of the earth will tend to alter the axis from its original 

 position. The gyroscope tends to respond, but, restricted by its 

 weight, which forces the axis to remain horizontal, it will undergo 

 only a horizontal displacement. 



This leads it to take a north and south direction, because as long as 

 its axis is not parallel to that of the earth, the cause of this movement 

 is still effective, so that if it is sufficiently free to move, it will indicate 

 true north. 



Plate 1 shows a model designed to show experimentally this action. 

 It consists of a small gyroscope, driven by a small three-phase elec- 



